In general, a joint using screw coupling can provide a secure and permanent piping, but has several problems in that it is inconvenient to screw and unscrew in a small place, and in that lots of time and manpower are required for piping.
To solve the above problems, a joint for plumbing using a wedge principle (hereinafter, referred to as a wedge type joint. The wedge type joint can complete coupling by inserting a pipe into the joint without any screw structure and deformation of the pipe. A conventional wedge type joint 10 is used in such a way that a stopper is inserted into an entrance of a spring whose the final round is formed in a trapezoidal shape. However, the conventional wedge type joint 10 is not great in tensile stopping power of a product because a contact surface between the stopper and the surface of the pipe is not maximized.
Furthermore, the wedge type joint has to apply power to make the pipe pass a packing when the pipe is inserted therein. For this, conventionally, a Y-ring, an O-ring, or two O-rings are put in the joint, and so, the conventional wedge type joint is larger than the present invention. In the above case, when the compressed rate of the packing is large, the joint provides an excellent sealability but it is difficult to insert the pipe. On the contrary, when the compressed rate is small, the pipe can be easily inserted, but sealability is deteriorated.
Moreover, the conventional joint additionally requires a cap for preventing introduction of dust or sewage when the joint is buried under the ground, but the wedge type joint can have the cap mounted thereon when the joint is buried under the ground as having no screw structure.